The potential reserves of liquid hydrocarbons contained in subterranean carbonateous deposits are known to be very substantial and form a large portion of the known energy reserves in the world. In fact, the potential reserves of liquid hydrocarbons to be derived from oil shale greatly exceed the known reserves of liquid hydrocarbons to be derived from petroleum. As a result of the increasing demand for light hydrocarbon fractions there is much current interest in economical methods for recovering liquid hydrocarbons from oil shale on commercial scales.
It has long been known that oil may be extracted by heat from various extensive deposits of porous minerals known by their generic term "oil shale", which are permeated by a complex organic material called "kerogen". Upon application of heat, the kerogen is converted to a complex mixture of hydrocarbons and hydrocarbon derivatives which may be recovered from a retort as a liquid shale oil product.
However, many oil shales, particularly the Devonian black shales of the eastern United States, contain large amounts of iron pyrites (FeS.sub.2). For example, a New Albany, Bullitt County, Ky. oil shale contains about 6% pyritic sulfur and 12% organic carbon. This pyrite is the cause of at least two serious problems in the winning of oil from the shales. At retorting temperatures, the iron pyrite reacts with the organic matter, generated from kerogen, robbing it of hydrogen, thus resulting in a poorer product and/or a lower yield of oils. Additionally, as a consequence of the foregoing reaction, large quantities of hydrogen sulfide are formed. Because of environmental considerations and due to the corrosive characteristics of hydrogen sulfide, the hydrogen sulfide has to be removed, for example, by converting it to sulfur.
Since the pyrite is uniformly distributed in the shale and the particle size is of the order of about 50 microns, mechanical separation and/or beneficiation to minimize the pyrite concentration are impractical if not impossible.